main.js

const $lis = document.querySelectorAll("ul li")
$lis.forEach((node) => {
    
    node.addEventListener("mousedown", function (event) {
        const value = node.innerText.trim()
        const $result = document.querySelector(".result")
        const resultText = $result.innerText.trim()

        if (resultText == "0" || resultText == "Infinity" || resultText == "undefined") {
            $result.innerText = ""
        }

        if (value == "=") {
            let solution = eval(resultText)
            $result.innerText = solution
            return true
        }

        if (value.toLowerCase() == "c") {
            $result.innerText = "0"
            return true
        }

        $result.append(value)
    })
})